One of the major factors limiting the operating life time of cryocoolers and other devices employing reciprocating piston compressors is contamination of the working gas volume by lubricants and other debris. For example, conventional Stirling cycle cryocoolers have a measured reliability of 300 hours MTBF. Four major failure modes have been identified in these cryocoolers: rotary bearing failure, compressor piston seal failure, contamination of the working gas volume by debris and lubricants, and helium leakage.
Seals, and in particular compressor piston seals, do not effect total sealing of the gas in the compression chamber portion of the working volume of the compressor. As a result, contaminant particles are transported into the compression chamber by gas Which escapes from that chamber past the seal, and which then returns to &he compression chamber as the compressor operates.
As an alternative type of seal, the use of bellows has been proposed, since a seal employing bellows is known to provide a nominally absolute seal, with gas leaking therepast at less than 0.0000001 cc helium/sec. The prior art, however, did not solve the problem of differential pressure across the bellows and as a result, in use such bellows underwent deformations which caused early fatigue failure.